A pulp treating vessel, such as a diffuser or a thickener, is shown in U.S. Pat. Nos. 4,793,161 and 4,881,286, which effectively backflushes screens within the vessel in an efficient manner to unclog the screens, without surge in the vessel volume. While the structure illustrated in said patents effectively performs the desired function, there are several possible minor drawbacks associated therewith. For example, the extraction arms may sag slightly due to the provision of an external actuator for the internal backflushing cylinder, and operation of the backflushing cylinder can be adversely affected if there is a tilting action between the internal screens and the top of the vessel.
According to the present invention, the potential minor problems discussed above are eliminated in a simple and effective manner that allows all the desirable results achieved by the structures of said U.S. Pat. Nos. 4,793,161 and 4,881,286 to be accomplished.
The pulp treating apparatus according to the invention comprises the conventional elements, in common with the structures illustrated in said patents, of a vessel, pulp inlet, pulp outlet, screen and supporting liquid conduits, extraction means, and an internal screen backflushing piston and cylinder. The invention differs from the prior constructions by providing the means for effecting actuation of the backflushing piston within the vessel. Preferably the actuator means comprises a second cylinder mounted on top of the arms that define the supporting liquid conduits for the screens, at a hub section thereof. The backflushing cylinder is mounted to the bottom of the arms at the hub, and a piston rod extends between the pistons associated with the cylinders. Hydraulic fluid is supplied to the actuating cylinder by fluid lines extending from the exterior of the vessel through a sealing conduit. The sealing conduit extends to a position above the top of the vessel so that should there be any hydraulic fluid leakage into the sealing conduit it will be indicated exteriorly of the vessel. A flexible bellows comprises part of the sealing conduit, preferably that portion attached directly to the hydraulic cylinder, to allow tilting action of the arms with respect to the top of the vessel.
The vessel is particularly adapted for pulp thickening, diffusion washing, and displacement bleaching, but may be utilized in other treatment systems which utilize screens that must be backflushed.
It is the primary object of the present invention to provide for efficient, reliable, and effective long term backflushing of screens in a pulp treatment vessel. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.